Chrysoprase, chrysophrase or chrysoprasus is a gemstone variety of chalcedony. It is a cryptocrystalline form of silica with traces of nickel. Its color may vary from apple-green to deep green. The darker varieties of chrysoprase are referred to as prase.

Chrysoprase is cryptocrystalline, which is composed of crystals so fine that they cannot be seen as distinct particles under normal magnification. This characteristic distinguishes it from the other varieties of crystalline quartz which are transparent and form six-sided crystals.

Agate, Carnelian and Onyx are some members of the cryptocrystalline silica family. It is the attractive color of chrysoprase, rather than any pattern of markings, that makes it very desirable. The word chrysoprase is derived from from the Greek ‘chrysos’ meaning ‘gold’ and ‘prasinon’, meaning ‘green’.

Emerald owes its green color to the presence of chromium. But the green color of chrysoprase is due to the presence of traces of nickel compounds in form of very small inclusions. The nickel reportedly occurs as different silicates, like kerolite or pimelite.

Chrysoprase results from the deep weathering of rocks. In the Australian deposits, chrysoprase occurs as veins and nodules. Chrysoprase measures 6 – 7 on the Moh’s scale of hardness. It has a conchoidal fracture like flint.

Chrome chalcedony is very similar to chrysoprase but its color is due to the presence of chromium rather than nickel. The best known sources of chrysoprase are Queensland, Western Australia, Germany, Poland, Russia, Arizona, California and Brazil.